The use of hydraulic pumps, such as power steering pumps, is well known in the automotive industry. Conventional hydraulic pumps, such as those used in power steering systems, are positive displacement pumps. Positive displacement pumps, such as gear pumps, have a pumping action that can create pressure fluctuations in the pump discharge flow. Any variations in this pump discharge flow are converted to pressure pulsations when they encounter circuit resistance. This conversion is referred to in the art as a pressure ripple.
One such example of a positive displacement pump is a vane rotor pump. During normal operation of pumps of this type, pressure pulsations are generated. Each rotation of the pump causes chambers that exist between the vanes to go through two expansion and compression phases, as is well known. The transitions between the expansion and compression phases can create pressure changes in the fluid which can create pressure pulsations. As the fluid is compressed, the pressure in the fluid builds up. This pressure can be different than the pressure in the pumping chamber at the high pressure side of the pump (outlet). Thus, when the compressed fluid at a higher pressure is added to the fluid in the pumping chamber, pressure pulsations can be created as the fluid equalizes in pressure as a whole.
The pressure pulsations transmitted through the fluid can cause resonating (vibrating) of the system components downstream of the pump. These pressure pulsations can also excite structure in the pumping circuit causing them to vibrate and generate additional objectionable noise. For example, if there is grounding of the hoses, i.e., direct contact of the hoses to the vehicle with no isolation, the system can create noises that are unacceptable to the vehicle user.
Typical pressure pulsation noises are tuned out by the use of various tuning methods in the hoses. The utilization of these tuning methods, however, is expensive. Additionally, accumulators have also been used as another possible way to tune out pressure pulsations. The use of accumulations, however, adversely affects the reaction time of the pump. It would therefore be desirable to provide a pump for use in a power steering system that is able to minimize pressure pulsations in an effective, cost efficient manner.